Frame transfer method and frame transfer device

ABSTRACT

A network enables a transfer path to be formed between nodes in the network so as to transfer frames. A terminal for transmitting frames located outside the transfer path, upon transmitting a frame through the transfer path, writes the transfer path selection information related to the transfer path and the output line information related to the output line from the terminating node of the transfer path in the frame according to the destination information set in the frame and transmits the frame to the destination. The starting node of the transfer path decides the transfer path used for transferring the frame according to the transfer path selection information set in the frame to transmit the frame while the terminating node of the transfer path decides the output line used to output the frame according to the output line set in the frame, thereby transmitting the frame to the output line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a frame transfer method, and moreparticularly to a frame transfer method employed for VPN services forrealizing virtual private networks (VPN).

2. Description of Related Art

There is a VPN service proposed for forming a virtual private network(VPN) in an enterprise by connecting a plurality of the enterprise sitesseparated physically away from one another. In recent years, another VPNservice has started. The new VPN service transfers frames according toMAC addresses, which are of the Ethernet (trademark). Each of this typenetworks is a comparatively small in scale and formed, for example,within an urban community and referred to as a MAN (Metropolitan AreaNetwork).

On the other hand, there is a technique for realizing a wide rangedlarge scale network configured by a plurality of such the MANs. Thistechnique is an application of the MPLS (Multi Protocol Label Switching)proposed, for example, in the IETF Draft “Encapsulation Methods forTransport of Layer 2 Frames Over IP and MPLS Networks”, draft-martini-12circuit-encap-mpls-04.txt referred to as the conventional technique 1and in the IETF Draft “Transport of Layer 2 Frames Over MPLS”,draft-martini-12 circuit-encap-mpls-08.txt referred to as theconventional technique 2. In those conventional techniques 1 and 2, apath referred to as a tunnel LSP (Label Switching Path) is formed in abackbone network connected to a plurality of MANs and a plurality ofpaths referred to as VC LSPs are formed in this path (tunnel LSP). Anode located at the inlet of the back-born network that connects theMANs adds a tunnel label and a VC label to each received frame. Both ofthe tunnel and VC labels are identifiers of those LSPs. And, the nodesin the back-born network transfer those frames while the node located atthe outlet of the back-born network processes the frames according totheir VC labels.

FIG. 2 shows a block diagram of a network to which such a conventionalframe transfer method applies.

Hereunder, the conventional techniques 1 and 2 will be described withreference to the block diagram of the network shown in FIG. 2. In thenetwork shown in FIG. 2, the sites LAN-A1 and LAN-A2 of an enterprise Aare connected to each other through MAN-1, MAN-3, and a backbone networkthat connects those MAN-1 and MAN3 respectively. The backbone network isconfigured by PEs (PE: Provider Edge Node) 1 to 3 located on the edgethereof and PCs (PC: Provider Core Node) 1 to 3. In the backbonenetwork, tunnel LSPs (T-LSP2 and T-LSP4) are formed. The T-LSP2transfers frames in the direction of PE1->PC2->PC3->PE3 while the T-LSP4transfers frames in the opposite direction. In the T-LSP2, a VC-LSP-A1is formed so as to transfer frames from the LAN-A1 to the LAN-A2. In theT-LSP-4, a VC-LSP-A2 is formed so as to transfer frames from the LAN-A2to the LAN-A1. In addition, another LSP used for communications betweeneach site of an enterprise B and each site of an enterprise C is formedin the backbone network. The LSP illustration is omitted in FIG. 2,however.

PE1 of the backbone network, when receiving a frame from the LAN-A1,adds a tunnel label that is the T-LSP2 identifier and a VC label that isthe VC-LSP-A1 identifier to the frame, then transfer the frame to thePC2. The PC2, as well as the PC3 refer to the tunnel label to transferthe frame to the PE3. The PE3 then refers to the VC label to transferthe frame to a line connected to the MAN-3. Consequently, the MAN-1 andis connected to the MAN-3, thereby the VPN service of the enterprise Ais realized.

Next, the problems of the conventional techniques 1 and 2 will bedescribed with reference to the network shown in FIG. 1, which is thesame as the network shown in FIG. 2. In FIG. 1 are shown only the LSPsformed among the sites of the enterprises A and B.

In the network shown in FIG. 1, the sites LAN-B1 to B4 of the enterpriseB are connected to one another through the MAN-1 to MAN-4, as well asthe backbone network that connects those MANs. In the backbone network,tunnel LSPs (T-LSP1 and T-LSP3) are formed. The T-LSP1 transfers framesin the direction of PE1->PC1->PE2 and the T-LSP3 transfers frames in theopposite direction. In the backbone network, other tunnels LSP (T-LSP2)and LSP (T-LSP4) are also formed. The LSP (T-LSP2) transfers framesPE1->PC2->PC3->PE3 and the LSP (T-LSP4) transfers frames in the oppositedirection. In the T-LSP1, a VC-LSP-B1 is formed so as to transfer framesfrom the LAN-B1 to the LAN-B2. In the T-LSP3, a VC-LSP-B3 is formed soas to transfer frames in the opposite direction. In the T-LSP2, aVC-LSP-B2 is formed so as to transfer frames from the LAN-B1 to theLAN-B3 and B4. In the T-LSP4, a VC-LSP-B4 is formed so as to transferframes in the opposite direction. In the backbone network are alsoformed still other LSPs; an LSP used for the communications among thesites of the enterprise A, an LSP used for communications among thesites of the enterprise C, and an LSP used for the communicationsbetween PE2 and PE3, although those LSPs are not shown in FIG. 1.

In a network configured as described above, the PE1, when receiving aframe from the LAN-B1, cannot decide to which of LAN-B2, B3, and B4 theframe should be transmitted. In other words, the PE1 cannot decide whichof the tunnels (VC-LSP-B1 in the T-LSP1 and T-LSP-B2 in the T-LSP2)should be used to transfer the frame through the VC-LSP. This is alsothe same for the PE3, which cannot decide which of the lines connectedto MAN-3 and MAN-4 should be used to transfer the frame. Consequently,the conventional techniques 1 and 2 described above cannot connect anysite over three or more MANs.

On the other hand, there is a technique for connecting a site over threeor more MANs. This technique enables the subject PE to learn an outputline number, a tunnel LSP, and a VC-LSP in accordance with the MACaddress set in each frame. Such the technique is known well as theconventional technique 3 (TETF Draft “Virtual Private Switched NetworkServices over an MPLS Network”, draft-vkompella-ppvpn-mpls-00.txt) andthe conventional technique 4 (IETF Draft “Transparent VLAN Services overMPLS”, draft-lasserre-vkopella-ppvpn-tis-00.txt). A PE, when receiving aframe from a PC belonging to the backbone network, stores transferinformation consisting of the line number of the line to which the frameis inputted, the tunnel LSP, and the VC-LSP therein in accordance withthe source MAC address set in the received frame. And, the PE, whenreceiving a frame from a MAN node, stores transfer informationconsisting of the line number of the line to which the frame is inputtedtherein corresponding to the source MAC address set in the frame. Whenreceiving a frame addressed to the stored MAC address, the PE transfersthe frame according to the transfer information corresponding to the MACaddress.

Next, the conventional technique 3 will be described in detail withreference to FIG. 1. The PE1, when receiving a frame from the terminalT7 belonging to the LAN-B3, stores the line number of the line connectedto the PC2, the VC-LSP-B2, and the T-LSP2 therein in correspondence withthe MAC address of the terminal T7. When the PE1 receives a frameaddressed to the terminal T7 from the MAN-1, the PE1 transfers the frameaccording to the line number, the VC-LSP-B2, and the T-LSP2 storedtherein as described above. The PE3, when receiving a frame from aterminal T7, stores the line number of the line to which the frame isinputted and the MAC address of the terminal T7 so that the line numberand the MAC address are corresponded to each other. And, the PE3, whenreceiving a frame addressed to the terminal T7 from the PC3, transfersthe frame to the line corresponding to the line number stored therein.

As described above, according to any of the conventional techniques 3and 4, when a frame is received from a MAN, it is possible to decide towhich of the remaining two or more MANs the frame should be transmitted.This is why a site can be connected over three or more MANs, thereby theproblems of the conventional techniques 1 and 2 are solved.

The conventional techniques 1 to 4 described above, however, are oftenconfronted with the following problem that will arise in construction ofa large scale network that comes to include many enterprises(contractors) connected over a plurality of MANs. The conventionaltechniques 1 and 2 also come to be confronted with another problem thata site connected over three or more MANs as described above cannot beconnected to a network that employs any of the conventional techniques 1and 2.

Furthermore, a network that employs any of the conventional techniques 3and 4 causes another problem to arise; the capacity of a table providedin each node to store transfer information often becomes insufficient.In other words, every PE that employs any of the conventional techniques3 and 4 is required to learn such transfer information as output linenumbers, tunnel LSPs, VC LSPs in correspondence with the MAC addressesof all the enterprises stored in the PE. For example, the PE1 shown inFIG. 1 is required to learn such the transfer information so as to makeit correspond to the MAC addresses of all the terminals T1 to T11 of theenterprises A to C. And, the table provided in such a PE so as to storesuch transfer information is limited in capacity and due to the limitedcapacity of the table, the networks that employ any of the conventionaltechniques 3 and 4 come to be disabled to store information of manyenterprises (contractors).

Under such circumstances, it is an object of the present invention toprovide a network that can hold information of many more enterprises(contractors) than any conventional networks by forming nodes on theedge of the subject network, which are used to store frame transferinformation corresponding to the destination address of each frame.

SUMMARY OF THE INVENTION

In order to solve the above conventional problems, the frame transfermethod of the present invention, employed for a network configured by aplurality of nodes and a plurality of terminals connected to one anotherthrough a line, enables a transfer path for transferring frames to beformed between nodes in the network, so that a node, upon receiving of aframe from a different node, writes a transfer path identifier used toidentify a target transfer path in the frame, thereby the frame istransferred to the destination. A terminal for transferring a receivedframe or node located outside the transfer path, when transmitting aframe through the transfer path, writes transfer path selectioninformation related to a target transfer path and output line selectioninformation related to an output line of the terminating node of thetransfer path in the frame according to the destination information setin the frame, then transmits the frame to the destination. The startingnode of the transfer path decides a target transfer path according tothe transfer path selection information set in the frame to transmit theframe to the transfer path while the terminating node of the transferpath decides a target output line according to the output line selectioninformation set in the frame, thereby transmitting the frame to theoutput line.

In another aspect, the frame transfer method of the present inventionforms a virtual line (e.g., a VC path) in the transfer path for eachlogical network formed in the network, so that a terminal fortransmitting a frame or node, which is located outside the transferpath, when transmitting the frame, writes a logical network identifierused to identify a target logical network in the frame, then transmitsthe frame. On the other hand, the starting node of the transfer pathdecides a target virtual line (a virtual line and an output lineconnected to the virtual line) according to the logical networkidentifier and the transfer path selection information set in the framewhile the terminating node of the transfer path decides a target outputline to output the frame therefrom according to the logical networkidentifier and the transfer path selection information set in the frame,thereby transmitting the frame to the output line.

In still another aspect, the frame transfer method of the presentinvention forms a virtual line (e.g., a VC path) in the transfer pathfor each logical network formed in the network, so that a terminal fortransmitting a frame or node, which is located outside the transferpath, when transmitting the frame, writes a logical network identifierused to identify a target logical network in the frame to transmit theframe. On the other hand, the starting node of the transfer path decidesa target virtual line (a virtual line and an output line connected tothe virtual line) according to the logical network identifier and thetransfer path selection information set in the frame, then writes thevirtual line identifier information (e.g., a VC label) used to identifythe virtual line in the frame to be transferred while the terminatingnode of the transfer path decides a target output line to output theframe therefrom according to the virtual line identifier information andthe output line selection information set in the frame, thereby enablingtransmission of the frame to the output line.

Further, the frame transfer device of the present invention is providedwith a plurality of input lines and a plurality of output lines and usedto transfer frames inputted to the plurality of input lines to theplurality of output lines. The frame transfer device also includes aframe information transmission unit for transmitting frame informationconsisting of one or both of the destination address information and thenetwork identifier set in the header of the frame, a transfer table forstoring a plurality of transfer entries, each storing destinationinformation consisting of at least one or both of the path selectioninformation and the output line selection information used by a frametransfer device located in the downstream of the frame transfer devicein a path connected to a terminal identified by the destination addressinformation to decide the destination of the frame, a header processunit for referring to the transfer table upon receiving the frameinformation to decide an output line number and destination informationcorresponding to the destination address information set in the headerof the frame, and destination information writing means for writing thedestination information in the frame.

In another aspect, the frame transfer device of the present invention,provided with a plurality of input lines and a plurality of output linesand used to output frames inputted from the plurality of input lines tothe plurality of output lines, further includes a frame informationtransmission unit for transmitting frame information to a destination,the frame information consisting of path selection information andnetwork identifier corresponding to the destination address informationwritten by a frame transfer device located in the upstream of the aboveframe transfer device, a transfer table for storing a plurality oftransfer entries, each consisting of an output line number and pathinformation corresponding to the frame information, a header processunit for referring to the transfer table upon receiving of the frameinformation to decide both of the output line number and the pathinformation, a frame switch for transferring the frame to the outputline corresponding to the output line number, and destinationinformation writing means for writing the path information in the frame.

In still another aspect, the frame transfer device of the presentinvention, provided with a plurality of input lines and a plurality ofoutput lines and used to output frames inputted from the plurality ofinput lines to the plurality of output lines, further includes a frameinformation transmission unit for transmitting frame informationconsisting of one or more of a network identifier, an input line numberthat is an identifier of the input line to which the frame is inputtedand path information that is an identifier of the path through which theframe is transferred, as well as output line selection informationcorresponding to the destination address information written by adifferent frame transfer device located in the upstream of the aboveframe transfer device; a transfer table for storing a plurality oftransfer entries, each consisting of an output line number correspondingto the frame information; a header process unit for referring to thetransfer table upon receiving of the frame information to decide atarget output line number; and a frame switch for transferring the frameto the line corresponding to the output line number.

In order to solve the above conventional problems, the frame transfermethod of the present invention, which is employed for a networkconsisting of a plurality of nodes and terminals connected to oneanother through a line, enables a transfer path for transferring framesto be formed between nodes in the network, so that one of the nodes,upon receiving a frame from a different node, writes a path identifierfor identifying a target transfer path in the frame and transmits theframe to the destination. A terminal for transmitting a frame or node,which is located outside the transfer path, when transmitting a framethrough the transfer path, writes the transfer path information relatedto the transfer path and the output line information related to anoutput line from the terminating node of the transfer path in the frameto be transmitted while the starting node of the transfer path decides atarget transfer path used for transferring the frame according to thetransfer path selection information set in the frame, then transmits theframe to the transfer path according to the destination information setin the frame. And, the terminating node of the transfer path alsodecides a target output line for outputting the frame therefromaccording to the output line information set in the frame, therebytransmitting the frame to the output line.

Concretely, a network that employs the frame transfer method of thepresent invention controls as follows so as to construct a large scalenetwork that can connect many enterprises (contractors). Concretely,each PE of the backbone network does not learn any such transferinformation as an output line number, a tunnel LSP, a VC LSP, etc.corresponding to each MAC address. Instead, a node located in theupstream of the PE adds information equivalent to such the transferinformation to transmit each frame. This added information includes aline to which the frame is transferred by a PE located at the inlet ofthe backbone network, a tunnel SP, VC LSP information, a line to whichthe frame is transferred by a PE located at the outlet of the backbonenetwork. Each PE transfers frames according to this information.

For example, if a frame is to be transferred from the LAN-B1 terminal T2to the LAN-B3 terminal T7, the frame will be transferred as follows. TheME located in the upstream of both PE1 and PE3, when receiving a frame,writes two pieces of information in the frame; the information forspecifying that the PE1 uses both T-LSP2 and VC-LSP2 in a line connectedto the PC2 and the information for specifying that the PE3 uses a lineconnected to the MAN-3 for transferring the frame. Then, the MEtransmits the frame to the destination.

A node required to store information corresponding to each MAC addresscannot have so many enterprises (contractors), since it comes to belocated at the side of the network edge. This is why such a node is justrequired to store only the information corresponding to the MAC addressof each terminal of those less enterprises. In the above example, theME2 stores information related to only the terminals of the enterpriseB, so that the ME2 comes to store information corresponding to the MACaddresses of the terminals (T2, T5 to T8, and T11). Consequently, thecapacity of the table for storing such the information does not preventthe increase of the number of contracted enterprises; the network thatemploys the present invention will thus be able to cope with many moreenterprises (contractors) than any other conventional networks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a network to which the frame transfermethod of the present invention applies;

FIG. 2 is a block diagram of a network to which a conventional frametransfer method applies;

FIG. 3 is a format of the DIX Ethernet frames transmitted by a terminalT2;

FIG. 4 is a chart for describing a table 1500 formed in a node ME2;

FIG. 5 is a chart for describing a table 1000 formed in a node ME2;

FIG. 6 is a format of frames handled in a MAN;

FIG. 7 is a chart for describing a table 1100 formed in a node MC;

FIG. 8 is a chart for describing a table 1200 formed in a node PE1;

FIG. 9 is a format of frames handled in a backbone network;

FIG. 10 is a format of a tunnel shim header 446;

FIG. 11 is a format of a VC shim header 447;

FIG. 12 is a chart for describing a table 2400 formed in a node PE3;

FIG. 13 is a chart for describing a table 1300 formed in each of nodesMC and ME2;

FIG. 14 is a format of frames handled in a MAN;

FIG. 15 is a format of frames handled in the backbone network;

FIG. 16 is a block diagram of a major portion of the node ME2;

FIG. 17 is a block diagram of a header process unit 1700 provided in theME2;

FIG. 18 is a format of frames handled in the node ME2;

FIG. 19 is another format of frames handled in the node ME2;

FIG. 20 is a block diagram of a major portion of each of the nodes PE1and PE3;

FIG. 21 is a block diagram of a header process unit provided in the nodePE1;

FIG. 22 is a format of frames handled in each of the nodes PE1 and PE3;and

FIG. 23 is another format of frames handled in each of the nodes PE1 andPE3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Next, an preferred embodiment of the present invention will be describedwith reference to the accompanying drawings.

FIG. 1 shows a block diagram of a network to which the frame transfermethod of the present invention can apply.

The network shown in FIG. 1 realizes VPN-A to C (VPN: (Virtual PrivateNetwork, A to C: enterprises A to C) in the VPN service. The VPN-A to Care connected to one another through a backbone network and a pluralityof MANs (Metropolitan Area Network) 1 to 6. The VPN-A is configured bysite LANs (Local Area Network) A1 and A2, the VPN-B is configured bysite LANs B1 to B4, and the VPN-C is configured by site LANs C1 and C2respectively. Each of the LANs is configured by a CE (Customer EdgeNode) used to connect the LAN to a MAN and one or more terminals T (T:Terminal). A MAN used to transfer frames between each LAN and thebackbone network is configured by an ME (MAN Edge Node) located at theedge and an MC (MAN Core Node) located at the core of the network. Thebackbone network connected to the MAN is configured by PEs (ProviderEdge Nodes) 1 to 3 and PCs (Provider Core Nodes) 1 to 3 located at thecore.

In the backbone network are formed a plurality of tunnel LSPs (LSP:Label Switching Path). In each of those tunnel LSPs, a T-LSP1 is formedso as to transfer frames in the direction of PE1->PC1->and PE2 while aT-LSP3 is formed so as to transfer frames in the opposite direction. Inaddition, a T-LSP2 is formed so as to transfer frames in the directionof PE1->PC2->PC3->PE3 and a T-LSP4 is formed so as to transfer frames inthe opposite direction. In the T-LSP1 is formed a VC-LSP-B1, which isused to transfer frames from the LAN-B1 to the LAN-B2, as well as aVC-LSP-B3 used to transfer frames in the opposite direction. And, in theT-LSP2 are formed a VC-LSP-B2 used to transfer frames from the LAN-B1 tothe LAN-B3 and B4, as well as a VC-LSP-B4 used to transfer frames in theopposite direction. In the tunnel LSP is also formed some other LSPsused for communications among the sites of the enterprise A, among thesites of the enterprise C, and between PE2 and PE3, although they arenot shown here.

When any of the conventional techniques 3 and 4 described above isemployed for the backbone network, the PE1 is required to store linenumbers, tunnel labels, and VC labels corresponding to the MAC addressesof the terminals T4 to T11, as well as line numbers corresponding to theMAC addresses of the terminals T1 to T3. Concretely, the PE1 of thebackbone network is required to learn and store such transferinformation as tunnel labels, VC labels, or line numbers correspondingto the MAC addresses of the terminals T1 to T11 of all the contractedenterprises. However, the table provided in the PE to store such thetransfer information is limited in capacity. The table thus becomes abottleneck sometimes in each network that employs any of theconventional techniques 3 and 4, so that it might be impossible to storemany contracted enterprises in the table.

On the other hand, in any network that employs the frame transfer methodof the present invention, the PE of the backbone network is not requiredto learn such transfer information as output line numbers, tunnel LSPs,VC LSPs corresponding to the MAC addresses. A node located in theupstream of the PE adds information equivalent to such the transferinformation to each frame to be transmitted. This added informationconsists of such information as line, tunnel LSP, and VC LSP used by thePE located at the inlet of the backbone network, as well as the subjectframe that stores information of the line number to which the frame isto be transferred by the PE located at the outlet of the backbonenetwork. Each PE transfers each frame according to this information.

In the frame transfer method of the present invention, each node thatstores information corresponding to the MAC address set in each frame islocated on the edge of the network. Therefore it does not need to storeso many contracted enterprises. Because such the node is just requiredto store information corresponding to the MAC addresses of not so manyterminals of each contracted enterprise, the capacity of the table forstoring such the information will thus not prevent the number ofcontracted enterprises from increasing.

Concretely, when the ME2 transfers a frame to the terminal T7 of theLAN-B3, the ME2 instructs the PE1 to specify lines connected to the PC2,the LSP-B2, and the T-LSP2. The ME2 also instructs the PE3 to specify aline connected to the MAN-3. At this time, the ME2 is just required tostore the LSP selection information and the output line selectioninformation as transfer information related to the terminals (T2, T5, T6to T8, and T11) of the enterprise B; the ME2 is not required to storeany transfer information related to the terminals of the enterprises Aand C.

Next, a description will be made for the operation of each node when theterminal T2 of LAN-B1 transfers frames addressed to the terminal T7 ofLAN-B3 with use of the frame transfer method of the present invention.

FIG. 3 shows a format of DIX Ethernet II frames transmitted by theterminal T2.

The DIX Ethernet II frame format consists of a header part 410, a datapart 420, and an FCS part 430.

The header part consists of fields of preamble 411, SFD (Start of FrameDelimiter) 412, source MAC address (SMAC: Source MAC) 413, destinationMAC address (DMAC: Destination MAC) 414, and type 415. The preamblefield 411 includes information for enabling a frame receiving device tofind the start of a frame and the SFD field includes information fordenoting the start of the frame. In those fields, hexadecimal values“01010101” and “AB” are set respectively. The SMAC field 413 sets thesource address of the frame while the DMAC field 414 sets thedestination address of the frame. The type 415 denotes a protocol of thenetwork layer stored in the data part 420. For example, “0800” (HEX)denotes that the received frame is a Novell NetWare frame. The data part420 consists of fields of data 421 and padding 422. The padding 422fills the space of the frame so that the frame becomes at least 64 bytesin full data length. The FCS 430 part has an FCS field 431. A device,when receiving a frame, checks this FCS field 431 to decide thevalidity/invalidity of the frame.

The ME2, when receiving a frame addressed to the terminal T7 from theterminal T2, identifies that the frame belongs to the enterprise Baccording to the line number of the line (hereinafter, referred to asthe input line number), through which the frame is received. Thisenterprise identification by the ME2 is realized by referring to a table1500 (FIG. 4) provided in the ME2 to read the VLAN ID 1501-i set in eachentry therein according to the input line number written in the frame.The table 1500 stores the VLAN ID, which is an enterprise identifier setfor each input line number.

The ME2 then decides a target output line (hereinafter, to be referredto as an output line number) from which the frame is to be output andthe destination site information according to the DMAC 414. Thisdecision of the output line number and the destination site informationis realized by referring to a table 1000 (FIG. 5) that stores bothoutput line number and destination site information in correspondencewith the MAC address of each terminal.

Concretely, the ME2 reads a plurality of entries 1010-i one by one fromthe table 1000 and compares the DMAC 414 set in the header part 410 ofthe frame with the MAC address 1002-i set in each entry to decide theline number 1001-i and the destination site information 1003-i set inthe “matching” entry 1010-i as both target line number and destinationsite information. This destination site information (two bits) consistsof single-bit LSP selection information 1013-i used to decide a targetLSP at the inlet PE1 of the backbone network and single-bit output lineselection information 1023-i used to decide an output line at the outletPE3 of the backbone network.

The ME2 then adds a header to the frame and transmits the frame to theMC (MAN Core). The added header includes the destination siteinformation bit for denoting whether or not the destination siteinformation 1003-i is valid. The destination site information 1003-iconsists of determined enterprise information (VLAN ID) and destinationsite information 1003-i. This header may be a VLAN Tag described in theIEEE 802.1Q.

FIG. 6 shows a format of frames transmitted from the ME2 and handled inthe MAN-1 after a VLAN Tag is added to each of the frames. In the frameformat shown in FIG. 6, a VLAN Tag 416 is inserted between the SMAC 413and the type 415 in the header part in the frame format shown in FIG. 3.

The TPID (Tag Protocol Identifier) 501 set in the VLAN Tag 416 is usedfor the Token Ring, FDDI, etc. When it is used by the Ethernet(trademark), it is represented as “8100” in hexadecimal. The CFI(Canonical Format Indicator) 503 is single-bit information used for theToken Ring communication. The UP (User Priority) 502 is 3-bitinformation denoting a transfer priority level. In this embodiment, thisUP 502 is used as LSP selection information 505 (1 bit) for storing LSPselection information, the output line selection information 506 (1 bit)for storing output line selection information, and the destination siteinformation bit 507 for denoting valid/invalid of both of the LSPselection information 505 and the output line selection information 506(1 bit). The VLAN ID 504 is an identifier of a VLAN (Virtual LAN). Inthis embodiment, it is used as an enterprise (VPN) identifier. The PE1writes the LSP selection information 1013-i, the output line selectioninformation 1023-i, and “1” (valid) in the LSP selection information505, the output line selection information 506, and the destination siteinformation bit 507 of the UP 502 respectively and writes the VLAN ID1501 corresponding to the enterprise B in the VLAN ID 504.

The terminals T2 or CE2 may be configured so that the information of theenterprise B is written in the VLAN ID 504 of the VLAN Tag 416 in eachframe to be transmitted. In this connection, the ME2 adds none of theenterprise identifier and the VLAN Tag 416 to the frame.

The MC in the MAN-1, when receiving such a frame, decides a targetoutput line number according to the DMAC 414 set in the frame andtransfers the frame to the output line. The ME3 transfers framessimilarly. Such the output line decision by the MC or ME3 is realized byreferring to a table 1100 (FIG. 7) that stores a plurality of entries1100-i, each storing a line number 1101-i and a MAC address 1102-i. TheMC or ME3 reads those entries 1110-i one by one from the table 1100 andcompares the MAC address 1102-i in each of the entries 1110-i with theDMAC 414 set in the header part 510 to decide the line number 1101-i inthe “matching” entry 1110-i as the target output line number.

The PE1, when receiving a frame through the MC or ME3, identifies theenterprise to which the frame belongs according to the VLAN ID 504 setin the header part 510 in the frame to decide that it is the enterpriseB. Then, the PE1 decides one or more sets, each consisting-of an outputline number, a VC LSP, and a tunnel LSP. The PE1 also selects one ofthose sets according to the LSP selection information 505 set in the UP502 of the header part 510. In this embodiment, the PE1 selects the set1 consisting of the line numbers of the lines to the PC2, a VC-LSP-B2,and the T-LSP2, as well as the set 2 consisting of line numbers of thelines to the PC1, the VC-LSP-B1, and the T-LSP1 according to the VLAN ID504, then decides the set 1 according to the LSP selection information505 as the information used for transferring the frame.

This decision is realized by, for example, referring to a table 1200(FIG. 8) that stores a plurality of entries 1210-i. The PE1 reads thoseentries 1210-i one by one from the table 1200 and compares theinformation written in the frame with that set in each entry so that theVLAN ID 504 set in the header part 510 of the frame is compared with theVLAN ID 1201-i set in each entry 1210-i and the LSP selectioninformation 505 set in the header part 510 of the frame is compared withthe LSP selection information 1202-i set in each entry respectively. ThePET then decides the line number 1204-i as the target output linenumber, the tunnel label 1205-i as the target tunnel label and the VClabel 1206-i as the target VC label, set in the “matching” entry 1210-irespectively.

The PE1 then adds the values of both tunnel label 1205-i and VC label1206-i to the frame to be transmitted to the backbone network.

FIG. 9 shows a format of the frames handled in the backbone network,transmitted by the PE1 after the header information related to bothtunnel label and VC label are added to each of the frames.

In the frame format shown in FIG. 9, a capsule header part 740 is addedto the frame and the fields of the preamble 411 and the SFD 412 aredeleted from the header part 510 of the frame format shown in FIG. 6,thereby forming the new header part 710. The capsule header part 740consists of the same fields 441 to 445 as those of the header part 510(FIG. 6), as well as a tunnel shim header 446, and a VC shim header 447.

FIG. 10 shows the tunnel shim header 446 formatted as described in theRFC 3032 and FIG. 11 shows the VC shim header 447 formatted as describedin the RFC 3032.

The tunnel shim header 446 consists of fields of tunnel label 801,experimental tunnel EXP 802, tunnel S bit 803, and tunnel TTL (Time toLive) 804.

Similarly, the VC shim header 446 consists of fields of VC label 901,3-bit VC EXP 902, VC S bit 903, and VC TTL 904. In this embodiment, thelower one bit of the VC EXP 902 is used for the output line selectioninformation 905 and the upper second bit is used for the VC EXPinformation bit 906 to be set for denoting valid/invalid of the outputline selection information 905. The MSB 907 is not used. The PET storesthe information of the tunnel label 1205-i and the VC label 1206-idecided above in the tunnel label 801 and in the VC label 901respectively.

Finally, the PET writes the value of the output line selectioninformation 506 (one bit) of the UP 502 in the output line selectioninformation 905 of the VC EXP 902 so as to notify the PE3 of the outputline selection information, then writes “1” (valid) in the VC EXPinformation bit 906. After this, the PET transmits the frame to the linecorresponding to the line number 1204-i.

The PC2 transfers the frame to the PC3 according to the tunnel label801, then updates the tunnel label 801. Similarly, the PC3 transfers theframe to the PC3 according to the tunnel label 801. The PC3 may deletethe tunnel shim header 446 at this time. When the header 446 is deleted,transmission of unnecessary information is prevented, thereby thenetwork band can be used more efficiently.

The PE3, when receiving this frame, identifies the enterprise to whichthe frame belongs according to both the input line number and the VClabel 901 to decide one or more target line numbers (a line to MAN-3 anda line to MAN-4 in this embodiment). The PE3 also decides the linenumber of the line to MAN-3 as the target output line number accordingto the output line selection information 905 set in the VC EXP 902.

The output line decision by the PE3 is realized by referring to a table2400 (FIG. 12) that stores a plurality of entries 2410-i, each storingan input line number 2401-i, a VC label 2402-i, a VC EXP 2403-i, and anoutput line number 2404-i. Concretely, the PE3 reads those entries2410-i one by one from the table 2400 and compares the informationwritten in the frame with that set in each entry 2410-i so that theinput line number in the frame is compared with the input line numberset in each read entry 2410-i and the VC label 901 set in the capsuleheader part 740 of the frame with the VC label 2402-i set in each entry,the output line selection information 905 set in the VC EXP 902 of theframe is compared with the output line selection information 2406-i setin the VC EXP 3403-i in each entry 2410-i to decide the output linenumber 2404-i in the “matching” entry as the target output line number.

The 3-bit VC EXP 2403-i consists of the output line selectioninformation 2406-i (1 bit), the VC EXP information bit 2407-i (1 bit)denoting valid/invalid of the VC EXP 2403-i, a non-used bit 2408-i (1bit). The value in this VC EXP information bit 2407-i is fixed at “1”.

After this, the PE3 deletes the capsule header part 740 (FIG. 9) fromthe frame and adds the preamble 411 and the SFD 412 to the header partof the frame, thereby the frame is formatted as shown in FIG. 6 and theframe is transmitted to the line corresponding to the output line number2404-i.

Each node in the MAN-3 decides the target output line number accordingto the DMAC 414 set in the header part 510 to transfer the frame to theLAN-B3 similarly to the MC in the MAN-1.

As described above, because both PE1 and PE3 are not required to storeinformation corresponding to the MAC address of each terminal, the tablefor storing such the information will not prevent the network fromexpanding in scale.

The information corresponding to the MAC address of each terminal may beset in the tables 1000 and 1100 from the administration terminalconnected to each node. When there are many terminals T and suchterminals T are often added/deleted to/from the network, such theinformation should be set in the tables 1000 and 1100 automatically.This auto setting of such the information is realized by making eachnode perform flooding, notifying, and learning operations. Hereinafter,these three operations will be described.

[Flooding]

If no entry 1010-i is set in the table 1000 (FIG. 5) formed in the ME2nor in the table 1100 (FIG. 7) formed in the MC in correspondence withthe DMAC 414 set in a frame transmitted from the T2 to the ME2, eachnode in the network transmits the frame to all the terminals T of thesame contractor (which, in the present embodiment, refers to anenterprise to which same VLAN ID is assigned).

Each node in a MAN decides one or more output line numbers to which theframe is to be transmitted according to the VLAN ID. Here, the MC in theMAN-1 is picked up as an example. Because only the LAN-A1 and the LAN-B1are connected to the MAN-1, the MC is just required to transmit theframes of enterprises A and B; it is not required to transmit the framesof the enterprise C. To transfer a frame of the enterprise A, therefore,the MC sets a line number connected to the ME1 for transferring theframe to the LAN-A1 and a line number connected to the ME3 fortransferring the frame to the LAN-A2 according to the VLAN-A2 of theenterprise A respectively. Similarly, to transfer a frame of theenterprise B, the MC sets a line number connected to the ME2 fortransferring the frame to the LAN-B1 and a line number connected to theME3 for transferring the frame to the LAN-B2 and LAN-B3 according to theVLAN ID of the enterprise B respectively. And, to realize such theoperations, the MC refers to a table 1300 (FIG. 13). The table 1300 isused for flooding operation and provided with a bit map 1310-i preparedfor each VLAN ID. Frame output YES/NO information is set in the outputline VLDj field 130 j-i located in the bit map 1310-i with respect toeach output line j.

At first, the flooding operation of the ME2 will be described. The ME2,when receiving a frame from the terminal T2, refer to the above table1500 ((FIG. 4) that stores a VLAN ID, which is an enterprise identifier,in correspondence with each input line number) to decide the VLAN ID.Then, the ME2 refer to the table 1000 ((FIG. 5) that stores both outputline number and destination site information in correspondence with eachMAC address). When the table 1000 includes no entry 1010-i correspondingto the DMAC 414 set in the frame, the ME2 reads the bit map 1310-i fromthe table 1300, corresponding to the VLAN ID of the enterprise B so asto perform a flooding operation. This bit map 1310-i stores data set soas to output the frame to a line connected to the MC and a line to theCE2 according to the VLAN ID of the enterprise B respectively. However,because there is no need to transmit the frame to the input line at thistime, the ME2 decides that only the line to the MC is the target outputline. And, because the ME2 cannot obtain no destination site informationat this time, the ME2 writes “0” (invalid) in the destination siteinformation bit 502, then transmits the frame to the MC.

Next, the flooding operation by the MC will be described. The MC, whenreceiving a frame from the terminal T2, refer to the table 1100 ((FIG.7) that stores a MAC address set in correspondence with each linenumber) similarly to the ME2. When the table 1100 includes no entry 1110corresponding to the DMAC 414, the MC reads the bit map 1310-i from thetable 1100, corresponding to the VLAN ID 504 of the enterprise so as toperform the flooding operation. Because no terminal of the enterprise Bis connected to any of the ME1 and the ME4, this bit map 1310-i storesdata needed to output the frame just to a line to the ME2 and a line tothe ME3 according to the VLAN ID of the enterprise B. However, becausethere is no need to transmit the frame to the input line here, the MCdecides that only the line to the ME3 is the target output line andtransmits the frame to the ME3.

The ME3, when receiving a frame from the terminal T2, also performs theflooding operation similarly.

Next, the flooding operation by the PE1 will be described. The PE1, whenreceiving a frame from the terminal T2, identifies “0” (invalid) set inthe destination site information bit 507 of the UP 502, thereby the PE1performs a flooding operation. In this flooding operation, the PE1transfers a copy of the frame to each of the output lines and LSPsconnected to the sites of the target enterprise (enterprise B in thisexample). This decision of all the output lines and LSPs by the PE1 isrealized by, for example, masking the LSP selection information 1202-i(regardless whether or not the “matching” is detected with respect toLSP selection information 1202-i) and referring to a table 1200 ((FIG.8) that stores a plurality of entries, each storing a line number, atunnel label, and a VC label). Concretely, the PE1 reads those entries1210-i one by one from the table 1200 and compares the informationwritten in the frame with that set in each entry so that the VLAN ID 504set in the header part 510 of the frame is compared with the VLAN ID1201-i set in each entry. The PE1 decides so that the frame istransmitted to the output line and the LSP specified by a set of a linenumber 1204-i, a tunnel label 1205-i, and a VC label 1206-i set in everyVLAN-ID-matching entry 1210-i, thereby transferring the frame to thedecided output line. At this time, the PE1 writes “0” (invalid) in theVC EXP information bit 906 of the VC EXP 902.

Next, the flooding operation by the PE3 will be described. The PE3, whenreceiving a frame in which the VC EXP information bit 906 “0” is set inthe VC EXP field 902, begins a flooding operation. In this floodingoperation, the PE3 identifies the enterprise to which the frame belongsaccording to the input line number and the VC label 901 set in the frameand decides one or more target output line numbers, then transmits acopy of the frame to all the lines corresponding to those output linenumbers.

For example, this decision of the target output line numbers is realizedby referring to the table 2400 ((FIG. 12) that stores a plurality ofentries, each storing an output line number) by masking the VC EXP2403-i (regardless whether or not “matching” is detected with respect tothe VC EXP 2403-i). Concretely, the PE3 reads those entries 2410-i oneby one from the table 2400 to compare the information written in theframe with that set in each entry 2410-i so that the input line numberwritten in the frame is compared with the input line number 2401-i ineach entry and the VC label 901 set in the capsule header part 740 ofthe frame is compared with the VC label 2402-i set in each entry. ThePE3 then decides the output line numbers 2404-i set in all theVC-label-“matching” entries 2401-i (line numbers of the lines to MAN-3and MAN-4 in this embodiment) as the target output line numbers andtransfer the frame to all the decided lines.

[Notifying Operation]

Next, the notifying operation for notifying the object of destinationsite information will be described.

The PE3, when transferring a frame addressed to the terminal T7 to theterminal T2, writes the output line selection information used totransfer the frame to the terminal T7 in the frame. The ME2 stores thisoutput line selection information corresponding to the MAC address ofthe terminal TV through a learning operation to be described later.

For example, the decision of this output line selection information isrealized by referring to the table 2400 ((FIG. 12) that stores aplurality of entries 2410-i, each storing an output line number).Concretely, the PE3 reads those entries 2410-i one by one from the table2400 to compare the information written in the frame with that set ineach entry 2410-i so that the input line number written in the frame iscompared with the input line number 2401-i set in each entry, the VClabel corresponding to the VC-LSP-B2 used for the frame transfer in theopposite direction of the VC-LSP-B4 is compared with the VC label 2402-iset in each entry, and the output line number used for the frametransfer is compared with the input line number 2401-i set in each entryto write the output line selection information 2406-i obtained from the“matching” entry 2410-i in the output line selection information field506 of the UP 502 of the frame.

On the other hand, the PE1, when transferring a frame addressed to theterminal T7 to the terminal T2, writes the LSP selection informationused for the frame transfer (LSP selection information corresponding tothe line number of a line connected to PC2, T-LSP2 and VC-LSP-B2) in theframe to be transferred to the terminal T2 through the terminal TV. TheME2 stores this LSP selection information in correspondence with the MACaddress of the terminal T7 through a learning operation to be describedlater.

The decision of this LSP selection information is realized, for example,by referring to the table 2400 (FIG. 12). Concretely, the PE1 readsthose entries 2410-i one by one from the table 2400 to compare theinformation written in the frame with that set in each entry 2410-i sothat the input line number written in the frame is compared with theoutput line number 2404-i set in each entry and the VC labelcorresponding to the VC-LSP-B2 is compared with the VC label 2402-i setin each entry, then writes the LSP selection information 2405-i (1 bit)obtained from the “matching” entry in the LSP selection information 506field of the frame.

[Learning Operation]

It should be avoided to always perform a flooding operation. Otherwise,the line bandwidth cannot be used efficiently. The MC thus performs alearning operation so as to store an input line number corresponding tothe source MAC address set in each inputted frame. On the other hand,the ME performs a learning operation so as to store destination siteinformation notified by the above notifying operation.

The MC, when receiving a frame, reads the entries 1110-i one by one fromthe table 1100 (FIG. 7)) that stores a MAC address in correspondencewith each line number) to compare the information written in the framewith that set in each entry 1110-i so that the input line number writtenin the frame is compared with the line number 1101-i set in each entryand the SMAC 413 written in the frame is compared with the MAC address1102-i set in each entry. When there is no “matching” entry 1110-i foundin the comparison, the MC registers the input line number and the SMAC414 written in the frame as new items 1101-i and 1102-i in an entry1110-i to be set in the table 1100.

Similarly, the ME2, when receiving a frame from the MC, reads theentries 1010-i one by one from the table 1000 ((FIG. 5)) that storesboth output line number and destination site information incorrespondence with each MAC address) to compare the information writtenin the frame with that set in each entry 1010-i so that the input linenumber in the frame is compared with the line number 1001-i set in eachentry, the SMAC 413 written in the frame is compared with the MACaddress 1002-i set in each entry, the LSP selection information 505written by the PE1 and output line selection information 506 written bythe PE3 in the frame are compared with LSP selection information 1013-iand output line selection information 1023-i in the destination siteinformation 1003-i set in each entry. And, when there is no “matching”entry 1010-i found in the comparison, the ME2 writes the items inputline number of the frame, 413, 506, and 505 specified in the frame as aline number 1001-i, a MAC address 1002-i, output line selectioninformation 1023-i, and LSP selection information 1013-i that are allset in an entry 1010-i to be registered in the table 1000. The PE in thebackbone network is not required to transfer any frame according to theDMAC 414, so that it does not perform such the learning operation.

While a description has been made for a case in which the ME2 mapsdestination site information in the UP 502 and the PE1 maps output lineselection information in the VC EXP 902, the fields of the UP 502 and VCEXP 902 might come to be too small in capacity to map destination siteinformation and output line selection information as described abovewhen the subject enterprise has many sites connected over many MANs.This is because the UP 502 and the VC EXP 902 are as small as 3 bits inlength. In such a case, the ME2 can add one more VLAN Tag and writedestination site information (LSP selection information and output lineselection information) in this VLAN ID 604 (12 bits). FIG. 14 shows sucha format of the frames to be transmitted from the ME2. Unlike the frameformat shown in FIG. 6, the frame format shown in FIG. 14 has aplurality of VLAN Tags 416 and 417. In FIG. 14, the VLAN Tag 417 is anew field added as described above.

Similarly, the PE1 can add one more shim header to the frame so as towrite output line selection information therein. FIG. 15 shows such aformat of the frames to be transmitted from the PET. Unlike the frameformat shown in FIG. 9, the frame format shown in FIG. 15 has three shimheaders. In other words, an extension shim header 448 is newly added tothe frame format.

Each node in the network operates in correspondence with such the headerconfiguration.

[Node: ME]

Next, a description will be made for the operation by the ME used in anetwork of the present invention with reference to FIGS. 16 and 17. FIG.16 shows a block diagram of a major portion of the ME2. FIG. 17 shows ablock diagram of a header process unit 1700.

In the embodiment to be described below, the LAN-B1 terminal T2transfers frames to the LAN-B3 terminal T7 and performs the floodingoperation.

As shown in FIG. 16, the ME2 is configured by a received frame processunit 1602-j provided to cope with a plurality of input lines 1601-j (j=1to M) to which frames are inputted, a transmit frame process unit 1604-jprovided to cope with a plurality of output lines 1605-j (j=1 to M) fromwhich frames are output, a header process unit 1700 used to process theheader part of each inputted frame, and a frame switch 1603 used toswitch frames among output lines. This header process unit 1700 analyzesthe header of each frame to decide the frame input enterprise (VLAN ID),the output line number, and the destination site information. The frameswitch 1603 switches frames among output lines according to the outputline number decided by the header process unit 1700.

[Transfer and Flooding Operations by ME2]

At first, a description will be made for a case in which the ME2receives a frame from the LAN-B1 CE2, then transmits the frame to theMC.

FIG. 18 shows a format of the frames handled in the ME2 in thisconnection. Unlike the frame format shown in FIG. 3, the frame formatshown in FIG. 18 has an internal header part 1840 added newly theretoand both of the preamble 411 and the SFD 412 are deleted therefrom,thereby forming the new header part 1810. This internal header part 1840consists of fields of input line number 1841, output line number 1842,destination site information 1843 (consisting of fields of LSP selectioninformation 1846 and output line selection information 1847),destination site information bit 1845 describing valid/invalid of thefield 1843, and VLAN ID 1844.

The received frame process unit 1602-j, when receiving a frame throughan input line 1601-j, deletes both preamble 411 and SFD 412 from theframe and adds the internal header part 1840 to the frame, then writesthe identifier “j” of the frame input line 1601-j in the input linenumber field 1841. Then, the received frame process unit 1602-j storesthe frame once therein and transmits the frame header information FH-jconsisting of the internal header part 1840 and the header part 1810 tothe header process unit 1700. The values of the output line number 1842,the destination site information 1843, the destination site informationbit 1845, and the VLAN ID 1844 set in the frame header information FH-jtransmitted to the header part process unit 1700 are all meaningless.

The header process unit 1700 decides the enterprise (VLAN ID) that hastransmitted the frame, the output line number, and the destination siteinformation (2 bits of LSP selection information and output lineselection information) with reference to the tables 1500 and 1000 (FIGS.4 and 5), then transmits the decided information to the received frameprocess unit 1602-j as destination information DI-j. The detailoperation of the header process unit 1700 is described later.

The received frame process unit 1602, when receiving destinationinformation DI-j, writes the information decided by the header processunit 1700 in the internal header part 1840 of the frame. In other words,the received frame process unit 1602 writes the VLAN ID of thedestination information DI-j in the VLAN ID 1844 of the internal headerpart 1840, the output line number is written in the output line number1842, the destination site information is written in the destinationsite information 1843, and the destination site information bit iswritten in the destination site information bit 1845 respectively. Then,the received frame process unit 1602 transmits the frame to the frameswitch 1603. The received frame process unit 1602, when receiving aplurality of pieces of destination information DI-j addressed to oneframe, copies the frame and transmits a copy of the frame to the frameswitch 1603. At this time, at least one of the VLAN-ID 1844, the outputline number 1842, and the destination site information 1843 must bedifferent from the original one set in the internal header part 1840.

The frame switch 1603 then transmits the frame to the transmit frameprocess unit 1604-j corresponding to the output line number 1842. Thetransmit frame process unit 1604-j deletes the internal header part 1840from and adds the preamble 411, the SFD 412, and the VLAN Tag 416 to theframe, thereby the frame format is updated as shown in FIG. 6. In otherwords, the process unit 1604-j writes the value of the VLAN ID 1844 inthe VLAN ID 504 of the VLAN Tag 416, the LSP selection information ofthe destination site information 1843 in the LSP selection information505 of the UP 502, the output line selection information 1847 of thedestination site information 1843 in the output line selectioninformation 506 of the UP 502, and the destination site information bit1845 in the destination site information bit 507 respectively to changethe frame format. The frame is then transmitted to the MC.

Next, the operation by the header process unit 1700 will be describedwith reference to FIG. 17.

The header process unit 1700, when receiving frame header informationFH-j from the received frame process unit 1602-j, stores the frameheader information FH with the frame header information storage. Theframe header information FH is obtained by multiplexing a plurality ofpieces of information FH-j through a multiplexer 1740.

A table access means 1721 of the VLAN ID decision unit 1720 reads anentry 1501-i corresponding to the input line number stored in the memory1760 from the table 1500 (FIG. 4) to decide the VLAN ID information,then transmits the decision result VI to both of the results output unit1750 and the table access means 1713.

The destination information decision unit 1710 refer to the table 1000(FIG. 5) to decide both the output line number and the destination siteinformation (LSP selection information and output line selectioninformation) corresponding to the DMAC 414 and transmits the destinationresult (information DI) to the results output unit 1750.

More concretely, the table access means 1711 of the destinationinformation decision unit 1710, when the frame header information FH isstored in the frame header information storage 1760, reads the entries1010-i one by one from the table 1000 and transmits the read entries1010-i to the comparator 1712. The comparator 1712 compares theinformation written in the frame with that set in each entry 1010-i sothat the DMAC 414 stored in the frame header information storage 1760 iscompared with the MAC address 1002-i set in each entry 1010-i andtransmits the result to the table access means 1711. This comparison isrepeated until it is completed for all the entries 1010-i in the table1000. Each time a “matching” entry is detected in the comparison, the“matching” denoting information is transmitted to the destinationinformation decision circuit 1714 together with the line number 1001-iand the destination site information 1003-i set in the entry 1010-i. Onthe other hand, the table access means 1713 reads the bit map 1310-istored in the table 1300 (FIG. 13) corresponding to the VLAN IDinformation VI decided by the VLAN ID decision unit 1720 and used forthe flooding operation, then transmits the result to the destinationinformation decision circuit 1714.

Receiving each “matching” denoting information from the table accessmeans 1711, the destination information decision circuit 1714 transmitsthe destination information DI to the results output unit 1750. In thisinformation DI, the line number 1001-i, the destination site information1003-i, and the destination site information bit “1” are set. Whenreceiving no “matching” information, the destination informationdecision circuit 1714 transmits the destination information DI to theresults output unit 1750. The information DI includes an output linenumber obtained by encoding the bit map 1310-i used for floodingoperation, which is received from the table access means 1713, thedestination site information “00”, and destination site information bit“0”. At this time, the destination information decision circuit 1714does not transmit the destination information DI with respect to the bitcorresponding to the input line number 1814 stored in the frame headerinformation storage 1760. When the bit map is described so as totransmit the frame to a plurality of output lines 1605-j, thedestination information decision circuit 1714 transmits a plurality ofpieces of the destination information DI to the results output unit1750.

Each time receiving destination information DI, the results output unit1750 transmits the values of the destination information DI and the VLANID as the destination information VI DI-j to the received frame processunit 1602-j corresponding to the input line number 1841 stored in theframe header information storage 1760. And, because the value of theVLAN ID information VI is decided by an input line number, the samevalue is always set in the plurality of pieces of the destinationinformation DI-j.

While a description has been made so far for a case in which the ME2recognizes the enterprise B and writes this information in the VLAN ID504, the terminal T2 and the CE2 may also write the information of theenterprise B in the VLAN ID 504 to transmit frames. In this connection,the frame format in the ME2 becomes as shown in FIG. 19. At this time,the VLAN ID decision unit 1720 does not decide the VLAN ID informationVI and the table access means 1713 reads the bit map 1310-icorresponding to the VLAN ID 504 stored in the frame header informationstorage 1760 and transmits the result to the destination informationdecision circuit 1714. The transmit frame process unit 1604-j does notoverwrite the information of the VLAN ID 1844 on the VLAN ID 504.

[ME2 Learning Operation]

Next, a description will be made for a case in which the ME2 receivesframes formatted as shown in FIG. 6 from the MC and performs thelearning operation. In this connection, an internal header part 1840 isadded to the format of the frames received by the ME2, thereby the frameformat comes to differ from that (shown in FIG. 6) of the frames in theME2. And, both preamble 411 and SFD 412 are deleted from the header part510 of the frame to form a new header part 1910 (as shown in FIG. 19).

At first, the operation by the header process unit 1700 will bedescribed. The header process unit 1700, when receiving frame headerinformation FH-j consisting of an internal header part 1840 and a headerpart 1910 from the received frame process unit 1602-j, stores the frameheader information FH obtained by multiplexing a plurality of pieces ofinformation FH-j through the multiplexer 1740 with the frame headerinformation storage 1760.

The destination information decision unit 1710 refers to the table 1000(FIG. 5) to check the presence of an entry 1010-i corresponding to theSMAC 413 written in the frame. When it is not found, the destinationinformation decision unit 1710 learns the input line number 1841, theLSP selection information 505 set in the UP 502, and the output lineselection information 506 corresponding to the SMAC 413.

More concretely, the table access means 1711 reads the entries 1010-ione by one from the table 1000 and transmits the read entries 1010-i tothe comparator 1712. The comparator 1712 compares the SMAC 413 stored inthe frame header information storage 1760 of the frame with the MACaddress 1002-i set in each entry 1010-i and transmits the result to thetable access means 1711. The table access means 1711 and the comparator1712 repeat the above operation until the comparison is completed forall the entries 1010-i in the table 1000.

When a “matching” entry 1010-i is detected, the table access means 1711decides that both line number and destination site informationcorresponding to the SMAC 413 are already stored in the table 1000,thereby terminating the learning operation. If no “matching” entry1010-i is detected, the table access means 1711 registers an entry1010-i in the table 1000. The new entry 1010-i includes the line number1001-i as the input line number 1841 stored in the frame headerinformation storage 1760 of the frame, the MAC address 1002-i as theSMAC 413 stored in the frame header information storage 1760 of theframe, the destination site information 1013-i of the LSP selectioninformation 1003-i as the LSP selection information 505 set in the UP502, and the output line selection information 1023-i of the destinationsite information 1003-i as the output line selection information 506 setin the UP 502 respectively.

[Node: PE]

Next, a description will be made for the operation by the PE1/PE3employed for the network of the present invention with reference toFIGS. 1, 15, 21, and 20. FIG. 20 shows a block diagram of a majorportion of the PE1/PE3. FIG. 21 shows a block diagram of a headerprocess unit 2300 (Both PE1 and PE3 are the same in configuration).

In the embodiment to be described below, it is premised that transferand flooding operations by the PE1 and PE3 for frames from the LAN-B1terminal T2 to the LAN-B3 terminal T7 and learning operations by the PE3and PE1 for frames from the terminal T7 to the terminal T2.

As shown in FIG. 20, the PE1 is configured by a received frame processunit 2002-k provided to cope with a plurality of input lines 2001-k (k=1to L) to which frames are inputted, a transmit frame process unit 2004-kprovided to cope with a plurality of output lines 2005-k from whichframes are output, a header process unit 2300 for processing the headerpart of each inputted frame, and a frame switch 2003 for switchingframes among output lines. The header process unit 2300 analyzes theheader of each frame to decide the output line number and the LSP. Theframe switch 2003 switches frames among output lines according to theoutput line number decided by the header process unit 1700.

[Transfer and Flooding Operations by PE1]

Next, a description will be made for the transfer operation by the PE1in response to a frame received from the ME3. The format of the framesin the PE1 (shown in FIG. 22) differs from that of the frames received(shown in FIG. 6). An internal header part 2140 is added to the frameformat in this case and the preamble 411 and the SFD 412 are deletedfrom the header part 510 of the frame format in FIG. 6 to form the newheader part 2110. This internal header part 2140 consists of fields ofinput line number 2141, output line number 2142, tunnel labelinformation 2143, VC label information 2144, and 3-bit VC EXPinformation 2145. This VC EXP information 2145 consists of fields ofoutput line selection information 2147, VC EXP information bit 2146 forsetting valid/invalid of the output line selection information 2147, anda field 2148 that is not used.

The received frame process unit 2002-k, when receiving a frame throughan input line 2001-k, deletes the preamble 411 and the SFD 412 from andadds an internal header part 2140 to the frame, then writes theidentifier of the input line 2001-k to which the frame is inputted inthe input line number field 2141 of the frame. The received frameprocess unit 2002-k then stores the frame once therein and transmits theframe header information FH-k consisting of the internal header part2140 and the header part 2110 to the header process unit 2300. In theframe header information FH-k, the values set in the output line number2142, the tunnel label information 2143, the VC label information 2144,and the VC EXP information 2145 are all meaningless.

The header process unit 2300 decides such target information as anoutput line number, a tunnel label information, a VC label information,and the VC EXP information according to the VLAN ID 504 of the UP 502set in the frame header information FH-k by referring to the table 1200or 2400 (FIGS. 8 and 12), then transmits the decided information to thereceived frame process unit 2002-k as the destination information DI-k.The operation of this header process unit 2300 will be described latermore in detail.

Receiving the destination information DI-k, the received frame processunit 2002-k writes the information decided by the header process unit2300 in the internal header part 2140 of the frame. In other words, thereceived frame process unit 2002-k writes the output line number of thedestination information DI-k in the output line number field 2142, thetunnel label information in the tunnel label information field 2143, theVC label information in the VC label information field 2144, and the VCEXP information in the VC EXP information field 2145 locatedrespectively in the internal header part 2140. The received frameprocess unit 2002-k then transmits the frame to the frame switch 2003.

The frame switch 2003 transmits the frame to the transmit frame processunit 2004-k corresponding to the output line number 2142. The transmitframe process unit 2004-k deletes the internal header part 2140 from theframe and adds a capsule header part 740 thereto to format the frame asshown in FIG. 9. Concretely, the transmit frame process unit 2004-kwrites the value of the tunnel label information 2143 in the tunnellabel field 801 of the tunnel shim header 446, the value of the VC labelinformation 2144 in the VC label field 901 of the VC shim header 447 andthe value of the VC EXP information 2145 in the VC EXP field 902respectively to change the frame format. After this, the transmit frameprocess unit 2004-k transmits the frame to the next node.

Next, the operation by the header process unit 2300 will be describedwith reference to FIG. 21.

The header process unit 2300, when receiving frame header informationFH-k from the received frame process unit 2002-k, stores the frameheader information FH obtained by multiplexing a plurality of pieces ofinformation FH-k through the multiplexer 2340 with the frame headerinformation storage 2360.

When the ME2 completes the learning and the UP 502 has a meaningfulvalue (“1” is set in the destination site information bit of the UP502), the destination information decision unit 2310 refers to the table1200 (FIG. 8) and transmits the output line number, the tunnel labelinformation, the VC label information, and the VC EXP informationobtained from the table in correspondence with both VLAN ID 504 and UP502 to the destination information decision circuit 2314. On the otherhand, when the ME2 does not complete the learning yet and the UP 502 hasa meaningless value (“0” is set in the destination site information bitof the UP 502), the destination information decision unit 2310 transmitsa set of one or more output line numbers corresponding to the VLAN ID504, the tunnel label information, the VC label information, and the VCEXP information to the destination information decision circuit

More concretely, the table access means 2311 of the destinationinformation decision unit 2310, when the frame header information FH isstored in the frame header information storage 2360, reads entries1210-i one by one from the table 1200 and transmits the read entries tothe comparator 2312. The comparator 2312, when “1” is set in thedestination site information bit, compares the information written inthe frame with that set in each entry 1210-i so that the VLAN ID 501stored in the frame header information storage 2360 of the frame iscompared with the VLAN ID 1201-i set in each entry 1210-i and the LSPselection information written in the frame is compared with the LSPselection information 1202-i set in each entry 1210-i. On the otherhand, when “0” is set in the destination site information bit, thecomparator 2312 masks the LSP selection information 1202-i (regardlessof whether or not “matching” is detected with respect to the LSPselection information) to make the comparison, that is, compares theVLAN ID 501 stored in the frame header information storage 2360 of theframe with the VLAN ID 1201-i set in each entry 1210-i and transmits theresult to the table access means 2311. The above comparison is repeateduntil it is completed for all the entries 1210-i in the table 1200.

And, each time a “matching” entry is detected in the comparison, thecomparator 2311 transmits the “matching” denoting information to thedestination information decision circuit 2314 together with the linenumber 1204-i, the tunnel label 1205-i, and the VC label 1206-i set inthe “matching” entry 1210-i. When “1” is set in the destination siteinformation bit, the comparator 2311 sets the 3-bit VC EXP informationto the lower one bit of the output line selection information 506 of theUP 502 and sets “1” in the upper second bit in the frame. The “1”denotes that the VC EXP information is valid. When “0” is set in thedestination site information bit, the comparator 2312 sets “0” (denotingthat the VC EXP information is invalid) in the upper second bit andtransmits the result to the destination information decision circuit2314. When “1” is set in the destination site information bit 507, thecomparator 2312 decides that “matching” is detected only in the entry1210-i to be transmitted to the VC LSP-B2 and the T-LSP2 in the lineconnected to the PC2. When “0” is set in the destination siteinformation bit 507, the comparator 2312 decides that “matching” is alsodetected in the entry 1210-i to be transmitted to the VC LSP-B1 and theT-LSP1 in the line to the PC1.

Each time receiving “matching” denoting information from the tableaccess means 2311, the destination information decision circuit 2314transmits the line number 1201-i, the tunnel label 1205-i, the VC label1206-i, and the VC EXP information to the object as the destinationinformation DI.

The results output unit 2350 transmits one or more pieces of thedestination information DI to the received frame process unit 2002-kcorresponding to the input line number 2141 stored in the frame headerinformation storage 2360 as the destination information DI-k.

[Notifying Operation by PE3]

Next, the notifying operation by the PE3 will be described.

The configuration of the PE3 is the same as that of the PE1 (FIG. 20).The PE3, when receiving a frame addressed to the LAN-B1 terminal T2 fromthe LAN-B3 terminal T7 through the MAN-3, not only transfers the framejust like the PE1 described above, but also decides the output lineselection information used for transmitting the frame addressed to theterminal T7 and writes the result in the frame to notify the ME2 of theoutput line selection information.

Consequently, the header process unit 2300 decides the output lineselection information used for selecting a line to the MAN-3 and addsthe output line selection information to the information DI-k intransfer operation by the PE1, then transmits the frame to the receivedframe process unit 2002-k. More concretely, each time the PE3 decides a“matching” entry 1210-i 1 in the above transfer operation, the tableaccess means 2311 reads the entry 1210-i 2 paired with the entry 1210-i1 and decides that the VC label 1206-i 2 set in the entry 1210-i 2 isthe target VC label 1 and the line number 1204-i 2 set in the entry1210-i 2 is the target output line number 1, then notifies thecomparator 2317 of the decision results.

To read such a pair of entries, for example, the table access means 2311is just required to assume the addresses of the entries 1210-i 1 and1210-i 2 as consecutive integers (2n and 2n+1) and read the entry1210-(i+1) from the address 2n+1 when it is decided that the address 2nmatches with that of the entry 1210-i and read the entry 1210-(i−1) fromthe address 2n when it is decided that the address 2n+1 matches withthat of the entry 1210-i. In addition, the table access means 2316 readsthe entries 2410-i one by one from the table 2400 and transmits the readentries 2410-i to the comparator 2317.

The comparator 2317 compares the information written in the frame withthat set in each entry 1210-i so that the input line number 2141 storedin the frame header information storage 2360 of the frame is comparedwith the input number 2401-i set in each entry 2410-i, the VC label 1written in the frame is compared with the VC label 2403-i set in eachentry 2410-i, and the output line number 1 written in the frame iscompared with the output line number 2404-i set in each entry 2410-i.The comparator 2317 then transmits the results to the table access means2316. The table access means 2316 and the comparator 2317 repeat theabove operation until the comparison is completed for all the entries2410-i in the table.

The table access means 2316 transmits the output line selectioninformation 2406-i set in the VC EXP 2403-i field of the “matching”entry 2410-i to the results output unit 2350 as the output lineselection information LSNI. The results output unit 2350 transmits theabove information to the received frame process unit 2002-k as a portionof the destination information DI-k.

The received frame process unit 2002-k writes this output line selectioninformation in the output line selection information field 506 of the UP502 in the frame and transfers the frame to the frame switch 1603.

[Transfer and Flooding Operations by PE3]

Next, how the PE3 transfers each frame received from the PC3 will bedescribed.

In this case, the frame format in the PE1 differs from that of receivedframes shown in FIG. 9. An internal header part 2140 is added to eachreceived frame and both preamble 411 and SFD 412 are deleted from thecapsule header part 740 to form a new header 2240 as shown in FIG. 23.

Receiving a frame through an input line 2001-k, the received frameprocess unit 2002-k adds the internal header part 2140 to the frame anddeletes the preamble 411 and the SFD 412 from the header part 2210 ofthe frame, then writes the identifier of the input line 2001-k to whichthe frame is inputted in the input line number field 2141 of the frameto change the frame format as shown in FIG. 23. The received frameprocess unit 2002-k also stores the frame once therein, then transmitsthe frame header information FH-k consisting of the internal header part2140, the capsule header part 2240, and header part 2210 to the headerprocess unit 2300. The header process unit 2300 decides the targetoutput line number according to the frame header information FH-k andtransmits the result to the received frame process unit 2002-k as thedestination information DI-k. The operation by this frame header processunit 2300 will be described later more in detail.

After this, the received frame process unit 2002-k writes the outputline number set in the destination information DI-k in the output linenumber field 2142 of the internal header part 2140 and transmits theframe to the frame switch 2003. The frame switch 2003 then transmits theframe to the transmit frame process unit 2004-k corresponding to theoutput line number 2142. The transmit frame process unit 2004-k deletesthe internal header part 2140 and the capsule header part 2240 from theframe and adds the preamble 411 and the SFD 412 to the frame to changethe frame format as shown in FIG. 6, then transmits the frame to thenext node.

Next, the operation by the header process unit 2300 will be describedwith reference to FIG. 21.

The header process unit 2300, receiving a plurality of pieces of frameheader information FH-k from the received frame process unit 2002-k,stores the frame header information FH obtained by multiplexing aplurality of pieces of information FH-k through the multiplexer 2340with the frame header information storage 2360.

The destination information decision unit 2310 refers to the table 2400(FIG. 12) to decide the target output line number. More concretely, thetable access means 2316 reads the entries 2410-i one by one from thetable 2400 and transmits the read entries 2410-i to the comparator 2317.The comparator 2317 then compares the information written in the framewith that set in each entry 2410-i so that, when “1” is set in the VCEXP information bit 906 located in the VC EXP 902, the input line number2141 stored in the frame header information storage 2360 of the frame iscompared with the input line number 2401-i set in each entry 2410-i, theVC label 901 stored in the frame header information storage 2360 of theframe is compared with the VC label 2402-i set in each entry 2410-i, andthe output line selection information 905 of the VC EXP 902 stored inthe frame header information storage 2360 of the frame is compared withthe output line selection information 2406-i of the VC EXP 2403-i set ineach entry 2410-i.

On the other hand, when “0” is set in the VC EXP information bit 906,the comparator 2317 masks the output line selection information(regardless of whether or not the output line selection informationmatches with the target) to make the comparison. In other words, thecomparator 2317 makes comparisons as described above so that the inputline number 2141 stored in the frame header information storage 2360 ofthe frame is compared with the input line number 2401-i set in eachentry 2410-i and the VC label 901 stored in the frame header informationstorage 2360 of the frame is compared with the VC label 2402-i set ineach entry 2410-i.

The comparator 2317 transmits the results to the table access means2316. The table access means 2316 and the comparator 2317 repeat theabove operation until the comparison is completed for all the entries2410-i in the table 2400.

Each time “matching” is detected in the above comparison with respect toan entry 2410-i, the comparator 2316 transmits the “matching” denotinginformation to the destination information decision circuit 2314together with the output line number 2404-i set in the “matching” entry2410-i. When the ME2 completes the learning and the VC EXP 902 has ameaningful value (that is, “1” is set in the VC EXP information bit906), the PE3 decides “matching” only in the entry 2410-i to betransmitted to the MAN-3. When the ME2 does not complete the learningand the VC EXP 902 has a meaningless value (that is, “0” is set in theVC EXP information bit 906), the ME2 also decides “matching” in theentry 1210-i to be transmitted to the MAN-4.

The destination information decision circuit 2314 transmits one or moreline numbers 2404-i received from the table access means 2316 to theresults output unit 2350 as the destination information DI. The resultsoutput unit 2350, each time receiving the destination information DI,transfers the information to the received frame process unit 2002-kcorresponding to the input line number 2141 stored in the frame headerinformation storage 2360 as the destination information DI-k.

[Notifying Operation by PE1]

Next, the notifying operation of the PE1 will be described.

The PE1, when receiving a frame addressed to the terminal T2 from theterminal T7, not only transfers the frame just like the PE3 describedabove, but also decides the LSP selection information used fortransmitting the above frame addressed to the terminal T7 and writes theresult in the frame to notify the ME2 of the LSP selection information.

Consequently, the header process unit 2300 decides the LSP selectioninformation and transmits the information to the received frame processunit 2002-k as a portion of the destination information DI-k. Moreconcretely, the table access means 2316 reads the entries 2410-i one byone from the table 2400 (FIG. 12) and transmits the read entries 2410-ito the comparator 2317. The comparator 2317 then compares theinformation written in the frame with that set in each entry 2410-i sothat the input line number 2141 set in the frame header informationstorage 2360 of the frame is compared with the input line number 2401-iset in each entry 2410-i and the VC label 901 set in the frame headerinformation storage 2360 of the frame is compared with the VC label2402-i set in each entry 2410-i. After this, the comparator 2312transmits the results to the table access means 2316. The table accessmeans 2316 and the comparator 2317 repeat the above operation until thecomparison is completed for all the entries 2410-i in the table 2400.

The table access means 2316 transmits the LSP selection information2405-i obtained from the “matching” entry 1410-i to the results outputunit 2350 as the LSP selection information LSPSI. At this time, the VCEXP 2403-i is masked, so that “matching” comes to be detected in aplurality of entries 2410-i in which the values of the VC EXP2 differsfrom each other. However, because the value of the LSP selectioninformation 2405-i in all those entries 2410-i are the same, the valuein any of those entries 2410-i may be transmitted to the results outputunit 2350.

The results output unit 2350 then transmits the LSP selectioninformation LSPSI to the received frame process unit 2002-k as a portionof the destination information DI-k. When it is required to transmit aplurality of pieces of destination information DI-k, each including aunique output line number, the same value is set in all those pieces ofthe LSP selection information.

The received frame process unit 2002-k writes the LSP selectioninformation set in the destination information DI-k in the LSP selectioninformation 505 of every frame to be transmitted to the frame switch1603, then transfers the frames to the ME2.

1. A frame transfer device, which is connected between a terminal fortransmitting a frame and a starting node of a transfer path in a networkdefined between the starting node and a terminating node of the transferpath through the network, comprising: a frame transmission/receptionunit for receiving the frame transmitted from the terminal; and a headerprocess unit for writing, in the received frame, transfer path selectioninformation for specifying a transfer path in the network to be used bythe starting node of the transfer path for transferring the receivedframe through the network, and output line selection information forspecifying an output line outside of the network to be used by theterminating node of the transfer path for outputting the transferredframe from the terminating node of the transfer path specified by thetransfer path selection information, wherein the frametransmission/reception unit transmits to the starting node the frame inwhich the transfer path selection information and the output lineselection information are written; the frame transmission/reception unittransmits, to the starting node, the transfer path selection informationcorresponding to a plurality of destination terminal addresses whichcorrespond to a plurality of said output line to which frames are to betransferred via the network, and the output line selection informationcorresponding to the plurality of destination terminal addresses fortransmission to the terminating node; the frame transfer device isconnected between the terminal for transmitting the frame and thestarting node of the transfer path; the network is a Multi-ProtocolLabel Switching (MPLS) network; and the frame transmission/receptionunit transmits from outside the MPLS network to the MPLS network whentransmitting the frame.
 2. A frame transfer device, which is connectedto a node for receiving a frame from a terminal, and which is connectedthrough a network to a plurality of terminating nodes of a transfer pathin the network, comprising: a frame transmission/reception unit forreceiving the frame transferred by the node; and a header process unitfor deciding a transfer path in the network to be used for transferringthe received frame through the network according to transfer pathselection information included in the received frame, the transfer pathselection information specifying the transfer path in the networkleading to a destination of the frame outside of the network, whereinthe frame transmission/reception unit transmits the received frame to aterminating node on the network of the transfer path in the networkdecided by the header process unit; the node is connected between theterminal and the frame transfer device; the transfer path selectioninformation is written in the frame by the node; the frametransmission/reception unit transmits, to a starting node on thenetwork, the transfer path selection information corresponding to aplurality of destination terminal addresses which correspond to aplurality of said destination of frames outside the network to whichframes are to be transferred via the network, and destination selectioninformation corresponding to the plurality of destination terminaladdresses for transmission to the terminating node; the network is aMulti-Protocol Label Switching (MPLS) network; and the frametransmission/reception unit transmits from outside the MPLS network tothe MPLS network when transmitting the frame.
 3. A frame transferdevice, which is connected to a node for receiving a frame from aterminal and to a starting node of a transfer path in a network, andwhich is connected to a terminal of destination of a frame, comprising:a frame transmission/reception unit for receiving the frame transmittedfrom the node for receiving the frame through the starting node of thetransfer path; and a header process unit for deciding an output lineoutside of the network to be used for transmitting the frame accordingto an output line information included in the received frame, the outputline information specifying the output line outside of the networkdecided from a destination of the frame, wherein the frametransmission/reception unit transmits the received frame to the terminalof destination of the frame through the output line outside of thenetwork decided by the header process unit; the node is connectedbetween the terminal and the frame transfer device; the output lineinformation is written in the frame by the node; the frametransmission/reception unit transmits, to the starting node, transferpath selection information corresponding to a plurality of destinationterminal addresses which correspond to a plurality of said output lineto which frames are to be transferred via the network, and output lineselection information corresponding to the plurality of destinationterminal addresses for transmission to the terminal; the network is aMulti-Protocol Label Switching (MPLS) network; and the frametransmission/reception unit transmits from outside the MPLS network tothe MPLS network when transmitting the frame.